Non-Volatile Memory Mode Switching for Long-Term Data Retention
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Solution Overview
Problem
The challenge of maintaining data retention in non-volatile memory cells over time due to changes in threshold voltage, which affects the reliability and longevity of data storage.
Innovation Solution
A memory system with a controller that switches between a normal mode and a long-term data retention (DR) guarantee mode, optimizing data retention by prioritizing stress tolerance and reducing write performance in the DR mode to ensure data can be read correctly over extended periods.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the memory system operates in normal mode with standard access operations, then write performance is maintained at acceptable levels, but data retention deteriorates over time due to threshold voltage changes
Solution Approach 1:
The memory system dynamically switches between normal mode and long-term data retention guarantee mode based on operational requirements. The controller adjusts access operation parameters in real-time, transitioning from standard performance-oriented operations to stress-tolerant operations when extended data retention is needed, and vice versa when write performance is prioritized.
Solution Approach 2:
The system changes operational parameters of access operations between two distinct modes. In normal mode, parameters are optimized for write performance with standard voltage levels and timing. In long-term data retention guarantee mode, parameters are adjusted to prioritize stress tolerance, including modified read/disturb parameters and program parameters that reduce threshold voltage drift, thereby extending the period during which data can be accurately read.
2Duration of action of stationary object
If access operations are optimized for long-term data retention, then the period for accurate data reading is extended, but write speed and performance are reduced
Solution Approach 1:
The memory system employs dynamic mode switching that allows it to adapt its operational characteristics based on current needs. When long-term data retention is required, the system transitions to a mode with extended retention parameters. When write speed is critical, it switches back to normal mode, providing flexible optimization without permanent performance degradation.
Solution Approach 2:
The controller modifies access operation parameters between modes to balance retention and speed. In long-term data retention guarantee mode, parameters such as read disturb margins, program verify thresholds, and refresh intervals are adjusted to maximize the retention period. These parameter changes inherently reduce write speed, but the system accepts this trade-off only when retention is the priority, otherwise operating in normal mode maintains higher write speeds.
3Reliability
If the memory system prioritizes stress tolerance to extend data retention, then reliability over time improves, but overall system performance decreases
Solution Approach 1:
The memory system dynamically adjusts its operational mode based on the specific requirements of the application. By switching between normal mode (optimized for performance) and long-term data retention guarantee mode (optimized for reliability), the system can prioritize stress tolerance only when extended data retention is needed, thereby maintaining high overall system performance while providing enhanced reliability when required.
Solution Approach 2:
The controller changes access operation parameters between two distinct operational states. In long-term data retention guarantee mode, parameters are modified to prioritize stress tolerance, including adjusted read/disturb parameters and program parameters that reduce threshold voltage changes. These parameter changes extend the retention period and improve reliability, but the system only operates in this mode when necessary, otherwise maintaining normal performance-oriented parameters.
Data Source
AI summary
A memory system includes a non-volatile memory having a plurality of memory cells and a controller. The controller is configured to switch a mode for controlling an access operation to the non-volatile memory from a first mode to a second mode, in response to receiving from a host, a first command for instructing the controller to switch the mode from the first mode to the second mode. The access operation controlled according to the second mode improves data retention relative to the access operation controlled according to the first mode.